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8da7cbf028
Re-ports this feature onto the pluggable-memory backend introduced in #4122 (the original #4143 was force-pushed clean by accident and auto-closed). The #4122 refactor moved the staleness logic into the self-contained DeerMem backend (backends/deermem/deermem/core/) and reverted it to the pre-feature global-threshold version, so the per-fact lifetime work is re-applied here against the new module layout + DI (MemoryUpdater is now (config, storage, llm)-injected; config lives on DeerMemConfig, not host MemoryConfig). **expected_valid_days (creation)** The LLM assigns a per-fact review window when storing each new fact. The prompt exposes five tiers (<=14 d transient -> >365 d very stable). The value is capped at write time by staleness_age_days x staleness_max_lifetime_multiplier (default 20.0 -> 1800 d ~= 5 years; range 1.0-100.0) so the model cannot set an initial lifetime so long the fact is never re-evaluated. The default 20.0 makes the "> 365 d very stable" tier achievable out of the box (3.0 silently clamped it to 270 d). **staleFactsToExtend (review)** During staleness review the LLM can emit extension entries for kept facts whose window seems miscalibrated. new_evd = min(days_since_created + extend_by_days, staleness_max_extension_days). Extensions use an absolute ceiling (default 3650 d ~= 10 years; range 90-36500) rather than the creation multiplier - they are deliberate review decisions that must be able to advance the window beyond the initial cap, but the absolute bound prevents timedelta overflow (a model-supplied extend_by_days of 10**9 previously crashed every later candidate-selection pass with OverflowError) and LLM misfire. **Invariant correctness** - Read-time cap removed from _effective_fact_staleness_age; cap is write-time only so extensions actually advance the review window. - proposed_remove_ids hoisted out of the removals sub-block and used to exclude from extension, so a cap-surviving proposed-removal fact is never extended. - extend_by coerced to int before the > 0 guard (a fractional 0.9 would pass the float check then int() to 0, silently writing a zero-delta extension). - days_since uses total_seconds() // 86400 (not .days truncation). - staleness-section html.escape uses quote=False to match the prompt.py convention; only <, >, & break element-text structure. **Tests** test_memory_staleness_review.py was module-level skipped by #4122 ("full unit-test migration is a follow-up"). This PR performs that migration: DI construction via (DeerMemConfig, _FakeStorage), _build_staleness_section back to the (candidates, config) signature, plus new coverage for per-fact selection, EXTEND with the absolute cap, the overflow next-cycle regression, the proposed-removal-not-extendable case, fractional extend_by skipping, and the creation-time cap. 67 tests, all green.